Sound isolation cabinet using two sound sources to generate complimentary sound waves

ABSTRACT

Two or more speakers are used to generate complimentary sound waves within a soundproof cabinet. The sounds generated inside the cabinet are detected by a microphone and sent to an external device for recording or listening purposes. In one embodiment, two speakers are arranged side-by-side and mounted on a panel. The panel serves to section off two chambers within the cabinet. The primary chamber is the chamber toward which the speakers are facing. The secondary chamber is the chamber within which the backs of the speakers are positioned. The speakers are connected to the input signal in reverse polarity of each other. Thus, during operation one speaker is pushing air outward while the other is pulling air inward. This complimentary generation of sound waves alleviates the muffling effect of the small isolated space and allows the speakers to generate sound as though they were in a much larger open area. Thus, the sound picked up by the microphone is very close to the desired “live” sound.

BACKGROUND OF THE INVENTION

[0001] This invention relates in general to sound isolation cabinetsuseful for recording musical instruments such as electric guitars, andmore specifically to a sound isolation cabinet using complimentary soundsources to generate improved isolated sound.

[0002] It is very difficult to accurately reproduce an electric guitar's“live” sound in an isolated space. However, it is very desirable to doso because isolating the sound allows the sound to be recorded withoutbothering other people such as neighbors in an apartment building. Also,isolating the sound prevents other sounds from interfering with therecording of the electric guitar sound as in professional recordingsituations where a live performance requires other loud instruments toplay at the same time as the electric guitar.

[0003] Two approaches have been made to isolate an electric guitarsound. One is the direct approach where the sound is maintained as apurely electronic signal. The other is the “isolation cabinet” approachwhere the sound is reproduced acoustically in an enclosed space.

[0004] The “direct” approach to recording electric guitars has beentried for many years. Many pre-amplifiers, equalizers and sound effectsgadgets are available to enhance the direct signal from the guitar sothat the processed signal can be directly used for recording, or forreproducing in headphones or for other purposes. However, none of theavailable direct equipment produces a sound as pleasing, or desired, asthe tone achieved when the electric guitar is played at amplified volumethrough speakers. Since this mode is the way the electric guitar isplayed in a live concert, it is sometimes referred to as the “live”sound of the electric guitar.

[0005] One reason the direct approach fails to reproduce the live soundis that there is a “speaker effect,” or coloration of the sound due tothe speaker or speakers. Different speakers have different sounds andare sought after for different types of music according to the tastes ofthe particular musicians. For example, speakers such as the “Greenback”speaker manufactured by Celestion International, Ltd., Foxhall Rd.,Ipswitch Suffolk, England, are very desirable for gritty, distorted“rock'n roll” tones. The number and variety of speakers is large. Eachadds a slightly different color to the tone. Apparently the complex waveeffects of the speaker cone's vibrating surface in air makes for a moreinteresting tone that is lost when using the direct approach.

[0006] Another reason that the direct approach fails to reproduce thelive tone of an electric guitar is that some guitar tones are only fullyrealized at high output from an amplifier. For example, amplifiers madeby Marshall Products, Ltd., Bletchley, England, are highly desirable forcertain types of music, but certain of their tones are only realizedwhen the amplifier's power output stage is set to a high output level.Although the prior art uses resistive loading, inductive loading andother techniques to try to “siphon” off a direct signal from anamplifier's power output, these methods fail to yield a sound that is,by many standards, even remotely close to the live sound.

[0007] Given the shortcomings of the direct approach, attempts have beenmade to produce “isolation cabinets” which are little more than enclosedboxes containing a speaker and a microphone. The electric guitar outputis amplified and fed to the speaker which produces sound that is pickedup by the microphone. The signals from the microphone are routed toother external devices for audibly playing the sound, or recording thesound. Since the electric guitar is amplified and driving a speaker,this setup is the same as the live setup. However, these approaches havefailed to produce a pleasing reproduction of the guitar tone. The reasonfor this is that the speaker is “damped” or restricted in it's freedomto vibrate because of the compression of air in a small volume necessaryto contain the sound. To date, no isolation cabinet exists that canapproach the live sound to the point where it can effectively be used torecord a certain live-sounding guitar tones in professional recordings.For example, the Internet page “www.cybtrans.com/guitar/g101.htm”includes a discussion on isolation cabinets, and the failings of somecommercially available cabinets.

SUMMARY OF THE INVENTION

[0008] The present invention is a sound isolation cabinet that uses twoor more speakers to generate complimentary sound waves within thesound-proof cabinet. The sounds generated inside the cabinet aredetected by a microphone and sent to external device for recording orlistening purposes. In one embodiment, two speakers are arrangedside-by-side and mounted on a panel. The panel serves to section-off twochambers within the cabinet. The primary chamber is the chamber towardwhich the speakers are facing. The secondary chamber is the chamberwithin which the backs of the speakers are positioned. The speakers areconnected to the input signal in reverse polarity of each other. Thus,during operation one speaker is pushing air outward while the other ispulling air inward. This complimentary generation of sound wavesalleviates the muffling effect of the small isolated space and allowsthe speakers to generate sound as though they were in a much larger openarea. Thus, the sound picked up by the microphone is very close to thedesired “live” sound.

[0009] A preferred embodiment of the invention uses: a cabinetenclosure; an input for receiving an external electrical signal; firstand second speakers positioned in the isolation cabinet, wherein thespeakers are responsive to the electrical signal to produce sound bymoving air within the cabinet; and a coupling between the input and thefirst and second speakers so that the air in the cabinet is moved in acomplimentary fashion to produce sound within the cabinet in response tothe electrical signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 shows a cutaway view of an embodiment of the presentinvention;

[0011]FIG. 2 is a schematic drawing of the configuration shown in FIG.1;

[0012]FIG. 3 is a schematic drawing of a second configuration; and

[0013]FIG. 4 is a schematic drawing of a third configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0014]FIG. 1 shows a cutaway view of a preferred embodiment of theinvention. Isolation cabinet 100 is shown with back 102 open forpurposes of illustration. This version of the cabinet was constructedusing a commercially-available speaker cabinet manufactured by JimMarshall Products, Ltd. It is a so-called “4 by 10” speaker cabinetwhich denotes that it originally housed four speakers whose diametersare approximately 10 inches, each. The particular shape of the cabinet,i.e., wider at the bottom and narrower at the top, is only due to thedesign of the original cabinet which was used to prototype the inventionfor practical reasons. Since the original cabinet was open-faced toallow the sound of the 4 speakers to emanate, a panel 104 was used tocover the openings.

[0015] The cabinet measures approximately 24″ high and 24″ wide. It is11″ deep at its base and 9.5″ deep at it's top. Mounting support panel106 is used to support speakers 108 and 110. The speakers are identical8 ohm, 10″ speakers manufactured by Celestion International, Ltd., withpart numbers G10L-35. The higher edge of the mounting panel is about 11″from the base of the cabinet while the lower edge of the mounting panelis about 3.5″ from the base. Thus, the speakers are inclined toward thefront of the cabinet. The angle of inclination is not critical. Also, noinclination needs to be used although the position illustrated producesgood tones and prevents matter from collecting in the speaker cones. Themounting panel spans the cross-section of the cabinet to create primarychamber 114 and secondary chamber 116. The preferred embodiment usesacoustic foam, approximately 1.5″ to 2″ thick, on all of the innersurfaces of the cabinet including back panel 102, but not on mountingsupport panel 106.

[0016] Microphone 112 is a Beta 57 microphone manufactured by Shure andis suspended by microphone cable so that its tip is about 2.5″ from thecenter of speaker 108. Input cable 120 couples to jack 122 to provide atwo-conductor input to the speakers. Note that the signal is applied ina first polarity to speaker 108, but is applied in reversed polarity tospeaker 110.

[0017] In operation, back panel 102 is secured to the isolation cabinetwith screws to create two chambers 114 and 116 that are sufficientlyacoustically sealed off from each other. An amplified electric guitarsignal is applied via input 120 to jack 122 so that speakers 108 and 110are driven. In the preferred embodiment, a 50-watt guitar amplifiermodel JCM-800 made by Jim Marshall Products, Ltd., is used. The signalis applied to speaker 108 in normal polarity, and is applied to speaker110 in reversed polarity. Thus, whenever the cone of speaker 108 pushesout in response to the sound signal, speaker 110's cone will pull in.This creates a complimentary pressure effect in primary chamber 114.Also, a complimentary signal is created in secondary chamber 116 in asimilar manner. Naturally, speaker 108 pulls in while speaker 110 pushesout so the effect is symmetrical.

[0018] The complimentary use of the two speakers, along with the dualchamber arrangement to alleviate the back pressure, reduces thedampening effect of moving air in a small enclosed volume. As a result,the guitar tones are produced in a fashion very close to the “live”sound, as where a speaker, or speakers, is used in the open air.Microphone 112 picks up the sound signal, primarily from speaker 108,and transmits the sound as an electrical signal through the microphonecable to external equipment (not shown). The external equipment can be,for example, a recording device, headphones, sound effects processors,etc. Thus, the present invention provides a way to obtain a livesounding isolated guitar tone for use in recording or for otherpurposes.

[0019] Note that many design tradeoffs are possible that deviate fromthe specific embodiment shown in FIG. 1. Naturally, many differentdimensions and shapes for the cabinet are possible. These can berectangular or curved. Many materials are suitable for constructing thecabinet. Many shapes for the chambers 114 and 116 are possible. Primarychamber 114 need not be larger than secondary chamber 116. The positionof microphone 112 may be anywhere in the cabinet, even in secondarychamber 116. In fact, by placing microphone 112 in different positionswithin the cabinet, different types of tones are emphasized. In theposition shown in FIG. 1, the resulting sound signals as transmitted bymicrophone 112 were found to be “bassy,” or strong in low frequencies.To compensate for this, the electrical signal is passed through anequalization unit to roll off the low end. Such modifications to thebasic sound are well known and are part of the artistry in recordingguitar tones that vary from musician to musician and among recordingengineers and producers.

[0020] The distance of the microphone to the speaker is easily regulatedby raising or lowering the microphone by its cable. In the preferredembodiment, the distances from the microphone to speaker 108 are markedon the cable itself. The cable is prevented from slipping by using aclamp or other means to secure the cable to the cabinet top (not shown).Many other ways to set the distance and position of the microphonerelative to the speaker are possible. By putting the microphoneuniformly between the speakers there may be advantages in tone or volumeregistering. Naturally, different types of microphones can be used toyield different tones, as is known in the art. A small microphoneelement can even be attached to the speaker cone itself, or affixed tothe wall (inner or outer) of the cabinet.

[0021] It is not necessary to line the inside of the cabinet withacoustic foam. In fact, a truer live guitar tone was produced when thefoam was not used. However, using the foam cuts down greatly on theamount of noise leaking out of the cabinet.

[0022]FIG. 2 shows schematically the arrangement of microphone, speakersand chambers of the embodiment of FIG. 1. Note that microphone 112,chamber 114, speakers 108, 110 and chamber 116 correspond to theiridentically numbered counterparts in FIG. 1.

[0023]FIG. 3 shows an arrangement where the speakers are connected inparallel, but in the same polarity. Speaker 202 is mounted in theopposite direction from speaker 204. Although feasible, this arrangementprobably will not produce tones as well as the arrangement of FIG. 2because the vibrating surfaces are not matched within each of thechambers 206 and 208. However, different microphone placements mightyield improved results. Note that the microphone can be placed in eitherof the chambers with identical results due to their symmetry. In thisrespect, the arrangement of FIG. 3 can be more suitable for a stereorecording where an additional microphone is used in front of speaker 202(not shown).

[0024]FIG. 4 shows yet another arrangement where the speakers 220 and222 are wired in opposite polarity but co-exist within a single chamber224. Although the microphone is placed closer to one of the speakers,interesting or more desirable results may be achieved with themicrophone in the center of the arrangement. The arrangement of FIG. 4is suitable for a small device. Indeed, with sufficiently small speakersand a microphone, the isolation cabinet can be made to fit into the palmof a hand, or smaller. Many other arrangements are possible.

[0025] Although the present invention has been illustrated with respectto specific embodiments as described herein, many modifications arepossible. For example, more than two speakers can be used as long asthey are arranged so that the air compression from one speaker iscompensated by a reaction from one or more of the other speakers. Insuch a case, the several speakers reacting to a main speaker might besmaller in size than the main speaker. By different arrangement ofchambers and shape of cabinet it may be possible to have three or morespeakers of the same or different size adequately compensate so thatsampling the sound from one or more of the speakers by optimummicrophone placement can yield superior results. More than 1 microphonecan be used and the resulting signals can be combined at later stagesfor improved sound, such as stereo sound, or for special effects. Aminiature version of the device can be built by using smaller speakers,microphone and cabinet enclosure. Also, electromagnetic coil speakers,like type described in the examples above, need not be used. Any audiotransducer, or means of moving air or another medium to produce soundscan be used with the present invention. For example, piezoceramicbenders, which are small flat plates without electromagnetic coils, canbe used to produce sound. The medium need not be air but can be anothergas.

[0026] Naturally, sound sources other than an electric guitar can beused. For example, the sound source can be a human voice; brass,woodwind, string or other instrument.

[0027] The scope of the invention is to be limited only by the appendedclaims.

What is claimed is:
 1. An isolation cabinet for producing sound, theisolation cabinet comprising: a cabinet enclosure; an input forreceiving an external electrical signal; first and second speakerspositioned in the isolation cabinet, wherein the speakers are responsiveto the electrical signal to produce sound by moving air within thecabinet; and a coupling between the input and the first and secondspeakers so that the air in the cabinet is moved in a complimentaryfashion to produce sound within the cabinet in response to theelectrical signal.
 2. The isolation cabinet of claim 1, furthercomprising: a microphone within the cabinet for detecting the soundproduced in the cabinet; and an output for transmitting signals from themicrophone to a device external to the cabinet.
 3. The isolation cabinetof claim 1, wherein the cabinet enclosure is substantially rectangular,the isolation cabinet further comprising: a mounting support for fixedlysecuring the two speakers within the cabinet, wherein the speakers aremounted side-by-side in the same facing direction; and the couplingincluding means to apply the electrical signal in a first polarity tothe first speaker, and in a second, opposite, polarity to the secondspeaker, so that when the first speaker moves in a first direction inresponse to the electrical signal, the second speaker moves in a second,opposite direction, in response to the same electrical signal.
 4. Theisolation cabinet of claim 3, further comprising: the mounting supportserving to divide the cabinet enclosure into first and second chambers,wherein the fronts of the speakers form one side of the first chamberand wherein the backs of the speakers form one side of the secondchamber.
 5. The isolation cabinet of claim 4, wherein the microphone islocated in the first chamber, wherein the microphone is positioned aboveone of the speakers.
 6. The isolation cabinet of claim 5, furthercomprising: sound insulation material lining part of the walls of theinterior of the cabinet enclosure.
 7. The isolation cabinet of claim 5,further comprising: support means for the microphone for fixing themicrophone position relative to the speakers.
 8. The isolation cabinetof claim 7, wherein the support means is a cable attached to themicrophone and passed through an opening at the top of the cabinet. 9.The isolation cabinet of claim 8, wherein the cable is adjustable tochange the distance of the microphone from the speakers.
 10. Anisolation cabinet for producing sound comprising: an enclosure; meansfor producing two or more complimentary sound waves within the enclosurein response to a sound signal source; and means for detecting the soundwaves within the enclosure.
 11. The isolation cabinet of claim 10,wherein the means for producing two or more complimentary sound wavesincludes a speaker.
 12. The isolation cabinet of claim 10, wherein themeans for producing two or more complimentary sound waves includes apiezoceramic bender.
 13. The isolation cabinet of claim 10, wherein themeans for producing two or more complimentary sound waves includes avibrating surface.
 14. The isolation cabinet of claim 10, wherein themeans for detecting the sound waves includes a microphone.
 15. Theisolation cabinet of claim 10, wherein the means for producing two ormore complimentary sound waves includes two speakers fixed in aside-by-side orientation within the enclosure.
 16. The isolation cabinetof claim 10, wherein the means for producing two or more complimentarysound waves includes two speakers in a face-to-face orientation withinthe enclosure.
 17. The isolation cabinet of claim 10, wherein the meansfor producing two or more complimentary sound waves includes twospeakers in an in-line orientation within the enclosure.
 18. Theisolation cabinet of claim 10, wherein the means for producing two ormore complimentary sound waves includes two sound sources, wherein themeans for detecting the sound waves includes a microphone near one ofthe sound sources.
 19. The isolation cabinet of claim 10, wherein themeans for producing two or more complimentary sound waves includes twosound sources, wherein the means for detecting the sound waves includesa microphone between the sound sources.
 20. An isolation cabinet forproducing sound, the isolation cabinet comprising: a cabinet enclosure;a panel dividing the enclosure into two chambers; first and secondspeakers mounted to the panel in a side-by-side arrangement so that thefronts of the speakers face into a first of the chambers while the rearsof the speakers protrude into the second of the chambers; and amicrophone fixed within the first chamber above one of the speakers withan output providing the signal generated by the microphone to anexternal device.